An electromagnetic fuel injection valve driven by an electrical signal from an engine control unit is used in an internal combustion engine of an automobile and the like. The electromagnetic fuel injection valve is configured to move a movable core so that a valve plug sits on a valve seat and leaves the valve seat for the purpose of accurately supplying fuel to the internal combustion engine and shutting off the supply of the fuel. A movable valve element, which comprises the movable core and the valve plug, can be moved by a magnetic attractive force generated between a stationary core and the movable core with an electromagnetic coil disposed around the stationary core and the movable core.
The movable core is attracted to the stationary core and leaves the stationary core by selective generation and non-generation of the magnetic attractive force, and an impact occurs between the movable core and the stationary core when the movable core is attracted to the stationary core.
Further, the movable core and the valve plug, which are engaged with each other, are configured so that they first are freed from each other and then impacts with each other, due to acceleration of them that is provided by the magnetic attractive force and a force of a return spring that presses the valve plug in a seating direction. In some of electromagnetic fuel injection valves, they have impact surfaces coated with a hard chromium film layer or the like to prevent them from being worn by such an impact.
Particularly, Patent Publication 1a discloses a method of coating end faces of the stationary core and the movable valve element, which includes the impact surface of the movable valve element, with a chromium film coat, and forming tapered surfaces on both the inner circumference side and outer circumference side of the impact surface for the purpose of reducing a liquid adhesion force between the stationary core and the movable valve plug, preventing the impact surface from being magnetized and providing improved response.